FIG. 1 shows a schematic diagram of a conventional power system 100 for an electric vehicle. The power system 100 includes a direct-current to direct-current (DC/DC) converter 106 and a rechargeable battery 104, and is used to power electrical equipment 102 in the electric vehicle. As shown in FIG. 1, the electrical equipment 102 is coupled to the DC/DC converter 106 and the battery 104 via a power input terminal 120, and is powered by the DC/DC converter 106 and/or the battery 104. Additionally, the DC/DC converter 106 may charge the battery 104.
The power system 100 may be problematic. By way of example, the electrical equipment 102 has a start-up threshold voltage, and does not operate if the voltage at the power input terminal 120 of the electrical equipment 102 is less than the start-up threshold voltage. Thus, if the voltage of the battery 104, e.g., provided as the voltage at the power input terminal 120, is less than the start-up threshold voltage, the DC/DC converter 106 will supply power only to the battery 104. The electrical equipment 102 is inactive until the battery 104 is charged to have a voltage greater than the start-up threshold voltage. Consequently, the power system 100 may take a relatively long time to start the electrical equipment 102.
Additionally, the DC/DC converter 106 may be plugged into the electric vehicle when the battery 104 is already well charged, and the voltage of the battery 104 may be greater than the output voltage VOUT of the DC/DC converter 106. A reversed current IR may flow from the battery 104 to the DC/DC converter 106, causing damage to the DC/DC converter 106.
Moreover, if the battery 104 is in an under-voltage condition, the battery 104 should be charged by a trickle current having a relatively small current level to avoid being damaged. However, the power system 100 does not provide such protection. That is, when the battery 104 is in the under-voltage condition, the DC/DC converter 106 may provide a charging current that is high enough to damage the battery 104.